Abstract: Introduction: Hutchinson-Gilford progeria syndrome (HGPS) is a rare, fatal, autosomal dominant premature aging disease with no approved treatment. It is caused by the production of progerin, an abnormal form of the inner nuclear membrane protein, lamin A. Progerin acts as a dominant negative. Because progerin is the only disease-causing protein in HGPS, its presence should be an indicator of the pathogenic process causing HGPS and decreased levels should indicate response to a therapeutic intervention. There is currently no validated biochemical biomarker for HGPS that can be obtained in the course of clinical trials for children with HGPS. This poses significant challenges to finding treatments and the cure for children with this fatal disease. We hypothesized that progerin would be detectible in biologic samples obtained from progerin-producing humans and mice. The PI and The Progeria Research Foundation contracted with EMD Millipore to develop a quantitative, sensitive, specific assay for progerin, and have developed a plasma progerin assay. A sandwich immunoassay using an ?-lamin A capture antibody and ?-progerin detection antibody was developed using SMC? and Erenna technology. Results: The assay has been characterized for sensitivity, specificity, spike recovery, dilutional linearity, intra- and inter-assay precision. Specificity: In samples spiked with known quantities of recombinant progerin and lamin A, progerin was detected at expected levels, whereas lamin A was not detected. Sensitivity: The assay Lower Limit of Quantification (LLoQ) has been repeatedly observed at 49 pg/mL. In addition, samples spiked with high-progerin plasma had recovery falling within the acceptance criteria of ?20% bias on each. Samples demonstrated parallelism of endogenous progerin between 5 and 125-fold dilution. Intra- and inter-assay precision is acceptable at ? 20% coefficient of variation. Homozygous (N=8) and heterozygous (N=11) BAC transgenic G608G mouse plasma progerin averaged 1,255,174166,353 and 476,173118,878pg/mL, respectively. Wild type mouse plasma progerin was undetectable. Plasma progerin levels decreased significantly when mouse models were treated with an RNA therapeutic or with the farnesyltransferase inhibitor, lonafarnib. Mean human nonHGPS and HGPS plasma progerin concentrations were 21581 (N=4) and 34,93217,859 (N=3) pg/ml, respectively. Progerin demonstrated stability over 4 x 30 minute freeze/thaw cycles. The treatment trial medication, lonafarnib, did not interfere with the assay results when added to patient plasma. Discussion: Progerin was detected in a quantitative, specific manner in HGPS plasma. Our overarching aim is to work with the FDA Biomarker Qualification group to establish plasma progerin as a pharmacodynamic biomarker of disease in HGPS. Success will greatly impact the ability to serially assess the effects of new potential therapies, leading to higher quality clinical trials with greater chance of effective treatment discovery.